1. Field of the Invention
This invention relates to a method and apparatus for locating objects buried in soil, for example underground utilities, using electromagnetic locators. More particularly, this invention relates to a method and apparatus for improving the precision of electromagnetic locators of underground utilities.
2. Description of Related Art
Utilities buried below the surface of the earth require periodic service and/or repair. Damaged utilities must be located and excavated in order to receive such service. However, location of underground utilities is a traditionally difficult task, particularly in areas containing large networks of underground pipes, wires and other buried objects.
Underground pipelines are generally constructed of either metal or, commonly, plastic such as polyethylene and polyvinyl chloride. Plastic is a preferred pipe material because it is durable, inexpensive, lightweight, inert, easy to manufacture and easy to install. To be detected with traditional underground pipeline location methods requires that the pipe be treated to impart a detectable feature into the plastic.
Electromagnetic locators to determine the location of buried objects such as underground utilities are well known in the art. By way of example, U.S. Pat. No. 6,586,937 B2 to Goodman teaches an apparatus for measuring and detecting a magnetic signature of a magnetically detectable object from a distance, which includes a portable sensor group for detecting the magnetic signature. However, conventional electromagnetic locators rely upon determining the depth and horizontal position of the buried object through the use of a model of a magnetic field that does not take into account all properties of the electromagnetic field and the environment surrounding the buried object. In particular, the model does not account for the time varying properties of the electromagnetic field nor does it account for the electromagnetic properties of the soil in which the buried object is located.